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7/28/2019 Week 10 Slide Note
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Transducers
- Classification and selection
- Primary Sensing Element
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Transducer
A measuring device, to convert none-
electrical variable into electrical
variable and vice versa
SensingElement
TransductionElement
Non-electricalquantity
SensorResponse
ElectricalSignal
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Classification:
1. Basic of transduction principle used
2. Active and passive3. Analog and digital
4. Primary and secondary
5. Common and inverse
Transducer
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Basic of transduction principle used
How the input variable is being converted intocapacitance or resistance or inductance values
Classification
http://www.google.com.my/url?sa=i&rct=j&q=resistive+transducer&source=images&cd=&cad=rja&docid=cUKdPRR-QIm5iM&tbnid=A3IaeZrsrDgu3M:&ved=0CAUQjRw&url=http://pubs.usgs.gov/twri/twri8a3/&ei=-3JvUaK3CM-zrAfw3YGIBQ&psig=AFQjCNE_np5uVHN8lw0x7QFGSmzUv1enHQ&ust=13663446886827927/28/2019 Week 10 Slide Note
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Active and Passive
No any external excitation to provide the
output.
Required an external excitation for passive.
Classification
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Analog and Digital
Producing the output in analog and digital formrespectively
Classification
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Primary and SecondaryMeasuring and converting a variable into
another variable and whose output forms the
input of another transducer.
Converting the output of first transducer into an
electrical signal.
Classification
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Usual and Inverse
Measuring and converting an electrical variable
into non-electrical variable
Classification
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Exercise !!!
What is a pressure transducer? A pressure transducer,sometimes called a pressure transmitter, is a transducerthat converts pressure into an analog electrical signal.Although there are various types of pressure transducers,
one of the most common is the strain-gage basetransducer. The conversion of pressure into an electricalsignal is achieved by the physical deformation of straingages which are bonded into the diaphragm of thepressure transducer and wired into a wheatstone bridge
configuration. Pressure applied to the pressuretransducer produces a deflection of the diaphragm whichintroduces strain to the gages. The strain will produce anelectrical resistance change proportional to the pressure.
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Selection1. Operating principle
2. Operating range
3. Accuracy4. Sensitivity
5. Stability and reliability
6. Usage and ruggedness
7. Transient and frequency response8. Loading effect
9. Electrical parameters
Transducer
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Operating principle
Basically the transducers are selected based on their
operating principle. Examples of operating principles
used by the transducers are resistive, capacitive,
piezoelectric, inductive, up to electronic principle etc.
Spec
Selection
http://localhost/var/www/apps/conversion/tmp/scratch_10/Manometer%20spec.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/Manometer%20spec.pdf7/28/2019 Week 10 Slide Note
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Operating range
This factor is considered so that the transducer should
be able to function within the specified range with
good resolution. Every transducer should be providedwith some rating within which there will be breakdown
in its function
Selection
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Accuracy
It is one of the most desired characteristic of any
transducer. If the transducer doesn't needs frequent
calibration, it must have high degree of accuracy and
repeatability. Because errors may occur due to the
sensitivity of the transducer to other stimulations
Spec
Selection
http://localhost/var/www/apps/conversion/tmp/scratch_10/Manometer%20spec.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/Manometer%20spec.pdf7/28/2019 Week 10 Slide Note
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Sensitivity
It is also a desired characteristic of a transducer. Every
transducer should be sufficiently sensitive to provide
some output that can be sufficient and detectable
Spec
Selection
http://localhost/var/www/apps/conversion/tmp/scratch_10/Force%20sensor%20spec.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/Force%20sensor%20spec.pdf7/28/2019 Week 10 Slide Note
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Stability and reliability
The transducer should have high degree of stability
during its function and also storage life. It should also
have a high degree of reliability
Selection
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Usage and ruggedness
The ruggedness, size and weight of a transducer should
be chosen depending on the application in which it is
used
Selection
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Transient and frequency response
The transducer should have required time domain
specifications such as, settling time, rise time, peak
over shoot and small dynamic error etc
Spec
Selection
http://localhost/var/www/apps/conversion/tmp/scratch_10/piezo%20spec.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/piezo%20spec.pdf7/28/2019 Week 10 Slide Note
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Loading effects
The transducers should undergo minimum loading
effect so that if can provide accurate measurement.The parameters of a transducer are that, which
characterize the loading effect is its input and outputimpedance. lt is considered in order to get minimum
loading effects (Which can be neglected). For minimumloading effect the transducer should have low output
impedance and high input impedance
Selection
http://localhost/var/www/apps/conversion/tmp/scratch_10/Force%20sensor%20spec.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/Force%20sensor%20spec.pdf7/28/2019 Week 10 Slide Note
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Electrical parameters
The type and length of cable required, signal to noise
ratio in case the transducer is used with amplifiers and
frequency response limitations should also be
considered
Spec
Selection
http://localhost/var/www/apps/conversion/tmp/scratch_10/Manometer%20spec.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/Manometer%20spec.pdf7/28/2019 Week 10 Slide Note
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Selection
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Sensing Element
Sensing
Element
Transduction
Element
Non-electrical
quantitySensor
Response
Electrical
Signal
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Capacitive Sensors- Consists of two parallel metal plates.
- There is either air or some others mediumbetween the plates (dielectric).
- Given,
- To detect displacement by applying moveableplates
- Capacitive displacement forms part of measuringpressure, sound or acceleration
- Also, can detect liquid level if the
dielectric is part liquid
Sensing Element
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Resistive Sensors
- Operating in variation of the resistance.
- Temperature measurement using thermistor.- Displacement measurement using
piezoresistive sensors
Sensing Element
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Magnetic Sensors
- Utilize the magnetic phenomena of
inductance, reluctance and eddy current.
- By moving the T core, current on the coil
changed.
Sensing Element
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Hall-Effect Sensors
- To measure the magnitude of a magnetic field.
- V = KIB, where K is known as Hall constant.- The magnitude of the field changes when the
device come close to any ferrous metal object
as application in proximity sensor.
Sensing Element
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Strain Gauges
- Changing in resistance when stretching andstraining.
- Able to detect very small displacement, 0-50m.
- Its consists of a length of metal resistance wire
formed into a zigzag pattern and mountedonto a flexible backing sheet.
- Gauge factor = R/S
Sensing Element
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Piezoresistive Sensors
- Made from semiconductor material, P-typeregion has been diffused into a N-type base.
- Producing higher gauge factor.
- Proper piezoelectric strain gauges also knownas semiconductor strain gauges.
Sensing Element
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Optical Sensors
- Air path, to measure proximity, translational orrotational motion and gas concentration.
- Fiber optic path, 2 major classes intrinsic andextrinsic sensors.
Sensing Element
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Ultrasonic Sensors
- The most common element is a piezoelectric
crystal.
- It can operate interchangeably as either a
transmitter or a receiver.
- The principle operation is an AC voltage
generates an ultrasonic wave and vice versa.
Sensing Element
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Nuclear Sensors- The basic operation is quite similar to optical sensor.
- Caesium-137 is used commonly as a -ray source,
and a sodium iodide device is used commonly as a -ray detector.
- To measure a level
of liquid in storage tanks.
Sensing Element
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Microsensors- In millimeter-sized, two and three-dimensional
micromachined structures.
- To measure temp, pressure, force, acceleration, humidity,
magnetic field, radiation and chemical parameters.- Usually, constructed from a silicon semiconductor material.
- Radiation microsensors are made from silicon p-n diodes oravalanche photodiodes.
Sensing Element
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Conclusion
Most non-electrical parameters can be
measured by electronic instruments. The
parameters will be detected and then
interpreted/converted to voltage or current informs of analog or digital techniques.
Combination of the task are operated using
transducers. Sometime, the operating withindividual device but others in cooperation.
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Thank You, See Again
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Spot Test
1. What is transducer?
2. Write the classifications of transducers?
3. What parameters should be considered in
selecting a transducer?
4. Write short notes on strain gauge sensor?